1. Field of the Invention
The present invention relates to a novel method and assembly for recording data at a very high density on phase-change media and phase-change media structures for this novel method.
2. Description of the Related Art
Conventional methods for reading and writing on a media include optical methods such as CD-ROM and magneto-optical (MO) storage devices. By focusing a laser beam to about one micrometer onto the storage media, one can read and sometimes record/erase information.
The density of an optical memory device is mainly diffraction limited. Specifically, with a focusing lens having a high numerical aperture, the corresponding radius of the focused beam spot cannot be smaller than half the illumination wavelength. Current commercial devices are already close to this resolution limit.
Magneto-optical recording methods use a focused laser beam as well to create a hot spot on a magnetic medium. The magnetic media, in turn, typically comprises a thin film magnetic media, which, at ambient temperature, has a high magnetic coercivity and is non-responsive to an externally applied magnetic field.
A conventional method for reading high density bits and apparatus therefor includes decoding high density data encoded in a digital recording media as a series of tags comprising an information bit pattern including a tracking bit pattern.
Several approaches have been demonstrated to improve on the resolution. First, more efficient lasers emitting shortened wavelengths may be used. Typically, a reduction of wavelength by a factor of two can be expected to provide a four fold increase in data storage density. However, the lasers required for such high storage densities are very expensive and further advances by reduction in the wavelength are not in the foreseeable future.
An approach for overcoming the diffraction limit uses evanescent waves, which can be confined due to their non-propagating properties to dimensions significant less than the wavelength of the laser. However, these methods often have poor signal-to-noise ratio, reliability and speed.